1. Field of the Invention
The present invention relates to a high-frequency transmission signal line and an electronic device, and more particularly to a high-frequency signal transmission line that transmits a high-frequency signal, and an electronic device.
2. Description of the Related Art
As a conventional high-frequency transmission signal line, for example, a signal transmission line disclosed by WO2011/007660 is known. The signal transmission line includes a laminate body, a signal line and two ground conductors. The laminate body is formed by stacking a plurality of insulating sheets. The signal line is disposed in the laminate body. The two ground conductors are disposed in the laminate body so as to sandwich the signal line with respect to the stacking direction. Thus, the signal line and the ground conductors form a strip-line structure.
The ground conductors have a plurality of openings in positions so as to overlap with the signal line, when viewed from the stacking direction. In positions where the plurality of openings are located, the capacitance generated among the signal line and the ground conductors is small. Accordingly, it is possible to shorten the distances in the stacking direction among the signal lines and the respective ground conductors without setting the characteristic impedance too low. Consequently, it becomes possible to produce a thinner high-frequency signal transmission line. Such a high-frequency signal transmission line is used, for example, to connect two circuit boards to each other.
In the high-frequency signal transmission line disclosed in WO2011/007660, however, since the ground conductors have openings, electromagnetic waves leak through the openings. Therefore, unnecessary radiation from the signal transmission line to the surrounding electronic devices occurs. When the signal transmission line is attached to a metal object such as a battery pack, the signal line and the battery pack are electromagnetically coupled via the openings. Consequently, the characteristic impedance of the signal line varies from the designed value.